1. Field of the Invention
The present invention relates to resistive sheets and pressure-sensitive switches used mainly for operating a range of electronic apparatuses, and to input devices using these resistive sheets and pressure-sensitive switches.
2. Background Art
In response to further advances in the functions and features of a range of electronic apparatuses, such as mobile phones and car navigation systems, resistive sheets, pressure-sensitive switches, and input devices using these sheets and switches that allow simple but wide-ranging operations are in demand for operating electronic apparatuses.
A conventional resistive sheet, pressure-sensitive switch, and input device using the sheet and switch are described below with reference to FIGS. 12 to 14. To facilitate understanding of their structures, dimensions in the thickness direction are enlarged in the drawings.
FIG. 12 is a sectional view, and FIG. 13 is an exploded perspective view of the conventional input device. In FIGS. 12 and 13, substantially dome-shaped movable contact 2 is attached to the bottom face of film over sheet 1 with adhesive (not illustrated).
Film cover sheet 3 is also flexible as over sheet 1. Movable contacts 2 are attached onto cover sheet 3 at five points, which are substantially in the center, and back, front, left, and right from the center, using over sheet 1.
Resistive layer 4 is formed by printing a material with a predetermined surface resistance. Film spacer layer 5 is provided on an area other than portions under movable contacts 2.
Cover sheet 3, and resistive layer 4 and spacer layer 5 on its bottom face configure resistive sheet 6.
Multiple wiring patterns (not illustrated) are formed, typically using copper foil, on the top and bottom faces of film-like or plate-like substrate 7. Semicircular fixed contacts 8A and 8B face each other with a predetermined space in between to configure fixed contact pair 8.
Fixed contact pairs 8 are disposed on substrate 7 at five points, which are substantially in the center, and back, front, left, and right from the center.
Controller 11 includes rated voltage supply 9, resistive element 10, and a microcomputer. Electronic circuit 12 including controller 11 is configured on the top face of substrate 7. Rated voltage supply 9 is connected to fixed contact 8A, controller 11 is connected to fixed contact 8B, one end of resistive element 10 is connected to fixed contact 8B, and its the other end is connected to grounding potential.
Resistive sheet 6 is disposed on fixed contact pairs 8 such that portions of resistive layer 4 not covered with spacer layer 5 face fixed contact pair 8.
Button 14 made of insulating resin is provided on substantially the center top face of rubber sheet 13 made of insulating resin. Operation frame 15 made of insulating resin is provided around button 14. Multiple press parts 13A on the bottom face of rubber sheet 13 contact the top faces of over sheets 1 at the centers of multiple movable contacts 2. Button 14 is disposed in a vertically movable manner and operation frame 15 is disposed in an oscillatable manner on rubber sheet 13 to configure an input device.
In the above structure, as shown in a perspective view of a conventional electronic apparatus in FIG. 14, rubber sheet 13 dents and presses movable contact 2, for example, if position S at the right side of operation frame 15 is pressed downward. Movable contact 2 then resiliently inverts downward with a clicking feedback. This dents resistive layer 4 downward, causing the bottom face of resistive layer 4 to make contact with fixed contacts 8A and 8B. Fixed contacts 8A and 8B are electrically coupled via resistive layer 4.
If further pressing force is applied, the area of resistive layer 4 making contact with fixed contacts 8A and 8B increases, so that resistance between fixed contact 8A and fixed contact 8B decreases.
Controller 11 in electronic circuit 12 formed on the top face of substrate 7 detects this change in resistance as a change in voltage by rated voltage supply 9 and resistive element 10. For example, controller 11 controls the moving direction or moving speed of cursor 19 for selecting from multiple menus 18 displayed on display unit 17 of electronic apparatus 16, such as a mobile phone.
If the upper right corner at position T is pressed, fixed contacts 8A and 8B in fixed contact pairs 8 at the right and back are electrically coupled via resistive layer 4. Controller 11 then moves cursor 19 diagonally upward to the right, and controls the moving speed.
In other words, cursor 19 moves correspondingly to the right if position S to the right edge of operation frame 15 is pressed. Similarly, if position T at the upper right corner is pressed, cursor 19 correspondingly moves to the upper right corner. If the pressing force is increased, cursor 19 moves faster. The electronic circuit controls these display operations.
One conventional art related to the present invention is Japanese Patent Unexamined Publication No. 2009-016330. In the above conventional input device, however, fixed contact pair 8 is provided only at five points: front, back, left, right, and center. Therefore, if a position even slightly to either side of position T is pressed, the timing of movable contact 2 making contact with fixed contact pair 8 deviates. As a result, the balance of the pressing force on each fixed contact pair 8 is poorly reproduced, failing to detect the pressing direction with sufficient accuracy. The cursor thus does not move precisely in the same direction as the pressing direction.